PENNY-PINCHING landlords had better watch out. Their tenants could soon be armed with thermal flashlights that capture a colourful – and possibly incriminating – portrait of a room’s temperature.

The device comes from the Public Laboratory for Open Technology and Science, a non-profit group based in Cambridge, Massachusetts, that develops open-source tools to allow ordinary people to investigate environmental issues. A PLOTS team is working with a school-run project in Harlem, New York, to help tackle landlords who offer poorly heated apartments.

Another PLOTS team is developing an underwater tool to detect river pollution. It will start by looking for warm sewage seeps in the Gowanus canal, a polluted New York City waterway.

Standard thermal cameras are prohibitively expensive for ordinary people. Costly sensors mean a camera with the resolution of a budget webcam can set you back thousands of dollars. That’s because each pixel represents a separate thermal probe.

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In contrast, the thermal flashlight prototype costs about &dollar;40. What’s more, it can easily be assembled by someone with no electronics expertise. To prove how easy it is, visitors to the Citizen Cyberscience Summit in London last month were shown how to build their own devices by fastening probes and wire to a circuit board. They used recycled VHS cases to house their creations.

“The thermal flashlight can be easily assembled by someone with no electronics expertise”

The thermal flashlight is built around a single infrared thermometer. This scans an area of wall and picks up varying levels of radiation emanating from it. This temperature information is fed into a microprocessor, which controls a multicoloured LED light. Shine the flashlight against a surface and the colour shows you a real-time temperature reading. Areas of the wall with a cooler temperature show up blue, while red light shines on patches that register as warmer. An image of the light-painted room showing exactly where heat is leaking can then be captured using a webcam with an online app called Glowdoodle or just standard time-lapse photography.

The team hopes that such pictures can be used to confront landlords who are not insulating their apartments sufficiently. In New York, for example, landlords must make sure their apartments are at 20 °C if the outdoor temperature falls below 12.8 °C between 6am and 10pm.

Users can tweak the code that controls the LED’s sensitivity so it responds to a narrower or wider temperature gradient.

The idea for the device grew out of a hack that created a glowing Roomba vacuum to monitor air quality. For Sara Wylie, a PLOTS co-founder who led the London session, such reincarnations are part of the lab’s citizen-science mission. The thermal flashlight has already led to the birth of different tools, with the Gowanus canal team developing a thermal fishing bob that directly measures water temperature while kept afloat by plastic bottles gathered from the canal itself.

While the device is sensitive enough to detect the temperature change when a cup of coffee is tipped into the water nearby, the team is now calibrating it so that it can detect much more subtle temperature changes. They intend to test the device on rainy days, when sewage sometimes overflows into the canal.

Jonathan Jesneck, at the Massachusetts Institute of Technology’s Field Intelligence Lab, says the flashlight is a “cute idea” that could perhaps be fused with results from the external drive-by thermal scans that he has worked on. “I really like the concept of empowering people to make thermal assessments of their own homes, without the need for expensive thermal cameras or software,” he says.

Wylie wants the project to spawn variations such as a device that maps dangerous levels of formaldehyde in the home. “What we see this tool as doing is basically giving a new kind of sensory access to the user,” says Wylie. “We don’t know all the questions it could be used to answer yet.”